This invention, relates generally to aircraft engines and more particularly to mounts for supporting an engine on an aircraft.
An aircraft engine may be mounted to an aircraft at various locations such as the wings, fuselage or tail. The engine is typically mounted at both its forward and aft ends by corresponding forward and aft mounts for carrying various loads to the aircraft. The loads typically include vertical loads such as the weight of the engine itself, axial loads due to the thrust generated by the engine, lateral loads such as those due to wind buffeting, and roll loads or moments due to rotary operation of the engine. The mounts must also accommodate both axial and radial thermal expansion and contraction of the engine relative to the supporting structure.
Engine mounts typically comprise a mounting frame that is fixedly secured to aircraft structure, such as a pylon, and a number of links that connect the engine to the mounting frame. In some applications, connecting links are required to be relatively long and slender components.
Long and slender mounting system components can have low order resonant frequencies that coincide with or are in close proximity to engine excitation frequencies, such as those caused by engine 1/rev operating speeds. These modes can be driven by inherent vibration caused by rotational unbalance in the low pressure or high pressure rotors of the engine. Because mounting systems tend to be lightly damped, high amplitude vibratory response is likely. High amplitude vibratory response can result in mount component high cycle fatigue, joint wear and/or repetitive impact damage.
Engine manufacturers typically rely on seeded unbalance testing to detect resonant frequency issues. Unfortunately, high engine unbalance events, such as rotor bladeout, cannot be practically tested because of the difficulty of producing high unbalance operation for a sufficient time to collect frequency data. This makes fielding a mounting system having tolerance to high engine unbalance a challenging task.
Currently, mounting systems are designed with component resonant frequencies that are not in proximity to engine excitation frequencies. This is typically accomplished by decreasing the length-to-diameter ratio of the link component in order to raise link flexure resonant frequencies sufficiently away from engine excitation frequencies to minimize the vibratory response. However, obtaining smaller length-to-diameter ratios generally results in larger volume mount links because the length of the links is often set by other design requirements. Larger volume links increase the overall weight of the mounting system and adversely affect packaging issues in a system where each part is usually allotted only a limited amount of space. Another possible approach is to accept the resonant link and design the links for high cycle fatigue endurance. This approach can be very difficult for new designs because link response to engine excitation is seldom known when the links are designed.
Accordingly, it would be desirable to have a link component for engine mounting systems that is designed with resonant frequencies that are not in proximity current links.